The overall goal of the proposed research is to test for genetic and environmental influences on brain structure in reading disability (RD) by performing morphometric analyses of MRI scans collected from RD and non-RD twin pairs. The specific goals of the proposed research are: 1.) To collect MRI scans from 20 twin pairs a year. When combined with the current sample, this will result in a total sample of 80 monozygotic (MZ) and 80 dizygotic (DZ) pairs in which at least one member of each pair will be reading disabled (RD) and 20 DZ pairs in which neither member will be RD. 2.) To perform state-of-the-art morphometric analyses, including cortical parcellation analyses, of these MRI scans targeting structures previously implicated in RD. These morphometric analyses will be performed without knowledge of subjects' diagnosis, relation, or zygosity. 3.) To conduct multivariate behavior genetic analyses of a.) the genetic and environmental components of variation in these morphometric measures and b.) their phenotypic and etiologic relations with behavioral measures. These analyses will be both confirmatory - by testing current strong hypotheses about brain-behavior relations in RD - and exploratory. 4.) To test whether the gene (s) influencing RD also influence brain structures which differentiate individuals with RD from controls. These analyses will use the methods in Research Project 4. 5.) To address basic issues in the new field of in vivo measurement of brain morphometry, such as relations among various brain structures and their relations to external variables, such as sex, age, and cognitive abilities.